Methods and devices for expanding a spinal canal

ABSTRACT

Devices and methods are disclosed for expanding a spinal canal. An implantable device having a shaft with a first cross-sectional dimension distinct from a second cross-sectional dimension can be inserted into an opening in a lamina and rotated 90 degrees to hinge the lamina away from the spinal canal. The implant can have one or more radiused edges, a bulleted tip, one or more lateral extensions for fastening the implantable device to bone, one or more hinged lateral extensions, one or more arcuate protrusions for biting into adjacent bone, an enlarged proximal head to prevent over-insertion, and/or a sleeve disposed therearound to reduce friction. Various embodiments of an insertion apparatus that can be selectively coupled to the implantable device are also disclosed, along with methods of expanding a spinal canal in minimally-invasive procedures using an implantable device and/or an insertion apparatus.

FIELD OF THE INVENTION

The present invention relates to methods and devices for use in surgery,and more specifically to methods and devices for expanding a spinalcanal.

BACKGROUND OF THE INVENTION

In certain pathologies, the spinal canal extending through a patient'svertebrae is or becomes too narrow and constricts the spinal cordextending therethrough. The narrowing may be congenital, potentiallyaffecting patients at any age. Narrowing can also be attributable toother causes, such as age, injury or removal of a spinal disc.

A condition associated with aging, for instance, is spondylolsis, inwhich intervertebral discs lose water and become less dense. Thesedegenerative changes near the disc can cause an overgrowth of the bone,producing bony spurs called, “osteophytes” that can compress the spinalcord. The constriction of the spinal cord in the cervical spine, forexample, often produces pain, weakness, or loss of feeling inextremities. Other causes for narrowing of the spinal canal include discshrinkage, which causes the disc space to narrow and the annulus tobulge and mushroom out, resulting in pressure on the spinal cord.Degenerative arthritis of facet joints can cause joints to enlarge, orthe vertebrae to slip with respect to each other, also compressing thespinal cord. Instability between vertebrae, such as caused by stretchedand thickened ligaments can also produce pressure on the spinal cord andnerve roots.

Myelopathy, or malfunction of the spinal cord, occurs due to itscompression. The rubbing of the spine against the cord can alsocontribute to this condition, and the spinal cord compression canultimately compromise the blood vessels feeding the spinal core, furtheraggravating the myelopathy.

Traditional procedures for decompressing the spinal cord include alaminectomy, in which the lamina and spinal processes are removed toexpose the dura covering the spinal cord. Laminectomies, however, canlead to instability and subsequent spinal deformity. Another knownprocedure is a laminoplasty, in which the lamina is lifted off the dura,but not completely removed. Typically, one side of the lamina is cut,while a partial cut is made on the other side to hinge the lamina awayfrom the spinal cord to increase the size of the spinal canal. A strutof bone can be placed in the open portion within the lamina and thefacet to help hold the open position of the lamina. Laminoplastiespreserve more of the bone, muscle, and ligaments, but current techniquesand devices are cumbersome and require exceptional technical skills,particularly for performing minimally invasive techniques.

Accordingly, improved methods and devices for expanding the spinal canalare needed, and in particular, methods and devices that can be used inminimally-invasive surgery.

SUMMARY OF THE INVENTION

The systems and methods disclosed herein can be useful for expanding aspinal canal. In one embodiment an implantable device is provided forexpanding a spinal canal. The implantable device includes an elongatebody having a head and a shaft. The shaft can have a cross-section takenperpendicular to the longitudinal axis of the body such that thecross-section has a first dimension distinct from a second dimension andhas at least two diagonally-opposite radiused corners. The head can havea driver interface at a proximal end thereof with a torque receivingsurface. In an exemplary embodiment, the cross-section of the shaft canbe substantially rectangular and the head can have a dimension largerthan the shaft to prevent over-insertion of the body into an opening.Additionally, the body can include an osteointegration-promoting coatingand/or can be formed of a resorbable material.

In another exemplary embodiment, the elongate body can have at least onearcuate protrusion formed thereon that is configured to engage bone asthe body is rotated within an opening. The body can also include atleast one lateral extension at its proximal end, the lateral extensionhaving at least one opening formed therein for receiving at least onefastening element. The at least one opening can have a variety ofcharacteristics. For example, it can be in the form of an elongate slotor a polyaxial seat. In one embodiment, the at least one lateralextension can be attached to the proximal end of the body with a hingesuch that the extension is rotatable about the hinge.

In another exemplary embodiment, the implantable device can include asleeve disposed around the body such that the body is rotatable withinthe sleeve.

In yet another embodiment, a method is provided for expanding a spinalcanal. The method can include forming an opening in a first side of alamina of a spine, inserting an implant into the opening in a firstorientation in which the implant fits within the opening in a clearancefit, and rotating the implant to a second orientation in which theimplant expands the size of the opening, thereby expanding the spinalcanal. The implant can be rotated in a variety of ways, and in oneembodiment it can be rotated 90 degrees. In an exemplary embodiment,rotating the implant can cause at least one arcuate protrusion formedthereon to engage a wall of the opening. Alternatively or in addition,rotating the implant can cause the lamina to cam over at least oneradiused corner of the implant.

In one embodiment, the implant can be inserted distally into the openinguntil a lip at the proximal end of the implant prevents furtherinsertion. The implant can be inserted into the opening using aninsertion apparatus selectively attached to the implant.

In another embodiment, the method can further include forming a reliefin a second side of the lamina opposite the first side before insertingthe implant to permit the lamina to hinge posteriorly away from thespinal canal. The method can also include accessing the vertebral bodyusing at least one minimally invasive portal and/or securing the implantto the vertebral body to prevent post-operative movement of the implant.Securing the implant can include unfolding at least one hinged lateralextension of the implant after inserting the implant into the openingand attaching the at least one hinged lateral extension to the vertebralbody with at least one bone screw.

In certain embodiments, inserting the implant can include firstinserting a sleeve into the opening and then inserting the implant intothe sleeve. Alternatively, inserting the implant can include insertingthe implant and a sleeve disposed therearound simultaneously.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more fully understood from the following detaileddescription taken in conjunction with the accompanying drawings, inwhich:

FIG. 1A is a perspective view of one embodiment of an implantable devicefor expanding a spinal canal;

FIG. 1B is an elevation view of the distal end of the implantable deviceof FIG. 1A;

FIG. 1C is a plan view of the implantable device of FIG. 1A;

FIG. 1D is an elevation view of the proximal end of the implantabledevice of FIG. 1A;

FIG. 1E is a cross-sectional view of the shaft of the implantable deviceof FIG. 1A;

FIG. 1F is an elevation view of the distal end of one embodiment of animplantable device having arcuate protrusions formed thereon;

FIG. 1G is a perspective view of the implantable device of FIG. 1F;

FIG. 2A is an elevation view of an implantable device and one embodimentof an insertion apparatus;

FIG. 2B is an elevation view of an implantable device and anotherembodiment of an insertion apparatus;

FIG. 3A is a plan view of a vertebral body and one embodiment of animplantable device partially inserted into an opening in a lamina;

FIG. 3B is a plan view of the vertebral body of FIG. 3A with theimplantable device fully inserted into the opening in the lamina;

FIG. 3C is an elevation view of the vertebral body of FIG. 3A with theimplantable device positioned in a first orientation within the openingin the lamina;

FIG. 3D is an elevation view of the vertebral body of FIG. 3A with theimplantable device rotated 90 degrees clockwise to a second orientationwithin the opening in the lamina;

FIG. 3E is a plan view of the vertebral body of FIG. 3A after theimplantable device has been rotated 90 degrees clockwise within theopening in the lamina;

FIG. 4A is a plan view of a vertebral body and one embodiment of animplantable device having a lateral extension;

FIG. 4B is a plan view of one embodiment of the lateral extension ofFIG. 4A;

FIG. 4C is a plan view of another embodiment of the lateral extension ofFIG. 4A;

FIG. 4D is a plan view of another embodiment of the lateral extension ofFIG. 4A;

FIG. 4E is a partial cross-sectional view of another embodiment of thelateral extension of FIG. 4A having a polyaxial fastener insertedtherethrough;

FIG. 5A is a plan view of a vertebral body and one embodiment of animplantable device having hinged lateral extensions;

FIG. 5B is an exploded plan view of one embodiment of a hinge;

FIG. 5C is an assembled plan view of the hinge of FIG. 5B;

FIG. 5D is a plan view of another embodiment of a hinge;

FIG. 5E is a plan view of the vertebral body and implantable device ofFIG. 5A with the hinged lateral extensions unfolded;

FIG. 5F is an elevation view of the implantable device of FIG. 5A withone embodiment of an insertion apparatus selectively coupled thereto;

FIG. 5G is an elevation view of the implantable device of FIG. 5A withanother embodiment of an insertion apparatus selectively coupledthereto;

FIG. 6A is a plan view of a vertebral body and one embodiment of animplantable device having a sleeve disposed therearound;

FIG. 6B is an elevation view of the vertebral body and implantabledevice of FIG. 6A;

FIG. 6C is an elevation view of the vertebral body and implantabledevice of FIG. 6A, after the implantable device is rotated 90 degreesclockwise;

FIG. 6D is a plan view of the vertebral body and implantable device ofFIG. 6A after the implantable device is rotated 90 degrees clockwise;and

FIG. 7 is a plan view of a spinal canal having been expanded using twoof the implantable devices of FIG. 5A.

DETAILED DESCRIPTION OF THE INVENTION

Certain exemplary embodiments will now be described to provide anoverall understanding of the principles of the structure, function,manufacture, and use of the devices and methods disclosed herein. One ormore examples of these embodiments are illustrated in the accompanyingdrawings. Those skilled in the art will understand that the devices andmethods specifically described herein and illustrated in theaccompanying drawings are non-limiting exemplary embodiments and thatthe scope of the present invention is defined solely by the claims. Thefeatures illustrated or described in connection with one exemplaryembodiment may be combined with the features of other embodiments. Suchmodifications and variations are intended to be included within thescope of the present invention.

In general, various devices and methods are provided for expanding aspinal canal by inserting an implantable device into an opening in alamina and rotating the implantable device to expand the opening. In oneexemplary embodiment, an implantable device for expanding a spinal canalis provided that includes an elongate body having a head and a shaft.The shaft of the elongate body can have a cross-section takenperpendicular to its longitudinal axis that has a first dimension toallow insertion between cut ends of a lamina that is distinct from asecond dimension sufficient to open and hold open a spinal canal. Forexample, the shaft can have a generally rectangular cross-section, canbe oval in cross-section, or can have virtually any othercross-sectional shape in which one dimension is greater than another.When a shaft having such a cross-section is inserted into an opening ina first orientation and then rotated 90 degrees about the axis ofinsertion to a second orientation, the opening can be spread apart orexpanded accordingly.

FIG. 1A illustrates one exemplary embodiment of an implantable device100 in accordance with the present invention. As shown, the implantabledevice 100 includes a head 102 and a shaft 104. The distal tip 130 ofthe shaft 104 can be bulleted or rounded to act as a wedge, therebyfacilitating insertion into a space having an initial dimension smallerthan the height Y of the shaft 104. The shaft 104 can also have one ormore radiused edges 103 to facilitate rotation within a bone opening, aswill be discussed in further detail below. In the illustratedembodiment, as shown in FIG. 1B, two diagonally opposed corners 103 ofthe otherwise rectangular shaft 104 are rounded or radiused. As shown inFIG. 1C, the head 102 of the device 100 can have a dimension larger thanthe shaft 104 such that it is configured to prevent over-insertion intoan opening. FIG. 1E illustrates a cross-section of the shaft 104 of theimplantable device 100. As shown, the shaft 104 has a cross sectionhaving a first dimension (i.e., width) X that is distinct from a seconddimension (i.e., height) Y.

As shown in FIGS. 1F-1G, the shaft 104 can optionally include one ormore protrusions 116 formed thereon configured to engage surroundingbone as the shaft is rotated within a bone opening. In the illustratedembodiment, the protrusions 116 are in the form of shallow arcuate finsangled in the direction of rotation and configured to superficially biteinto the interior walls of the bone opening as the shaft is rotatedtherein. The protrusions 116 can also be angled opposite to thedirection of rotation or there can be some protrusions angled in onedirection while others are angled in the opposite direction.

As shown in FIG. 1D, the head 102 of the implantable device 100 caninclude a driver interface 106 at a proximal end thereof with a torquereceiving surface that is configured to permit selective coupling of theimplantable device 100 to an insertion apparatus. The driver interface106 can be either male or female. For purposes of illustration, FIG. Dshows a female driver interface 106.

FIG. 2A illustrates one embodiment of an insertion apparatus 108 forinserting the implantable device 100 into a patient using a minimallyinvasive procedure. As shown, the insertion apparatus 108 can be in theform of an elongate body 110 having a handle portion 112 and a trigger113 at its proximal end and an engagement member 114 at its distal end.The handle 112 and/or the elongate body 110 can be bayoneted or angledto improve visualization and/or ergonomics during a surgical procedureand can be sized to permit delivery of the implantable device through anaccess port in a minimally invasive procedure. In the illustratedembodiment, the engagement member 114 is in the form of a maleprotrusion 115 configured to selectively engage a female socket 106formed in the head 102 of the implantable device 100. The protrusion 115can selectively engage the socket 106 using any of a variety oftechniques known in the art, including for example a friction fit, aninterference fit, a threaded engagement, etc. In the illustratedembodiment, a small piston 117 is positioned in one side of theprotrusion 115. The piston 117 can be actuated by the trigger 113 suchthat squeezing the trigger 113 can retract the piston 117 into theprotrusion 115, thereby removing a friction or interference engagementof the piston 117 with a sidewall of the socket 106. Releasing thetrigger 113 can be effective to force the piston 117 back out of theprotrusion 115 and into a friction or interference engagement with thesocket 106. The protrusion 115 can have a non-circular cross-sectionsuch that rotation of the insertion apparatus 108 causes a commensuraterotation of the implantable device 100 when the two are coupledtogether.

FIG. 2B illustrates another embodiment of an insertion apparatus 108′.As shown, the engagement member 114′ of this embodiment includes opposedclaws configured to grasp the edges of the head 102 of the implantabledevice 100. Squeezing the trigger 113′ proximally towards the handle112′ can be effective to draw the claws together. Releasing the trigger113′ can be effective to spread the claws apart. One skilled in the artwill appreciate that various other methods of selectively engaging theimplantable device with an insertion apparatus can be used.

The implantable device can be formed of a variety of implantablematerials, including resorbable materials, non-resorbable materials,and/or a combination thereof. The implantable device can be radiopaqueto facilitate accurate insertion of the device in a minimally invasivesurgery using fluoroscopy, can be radiolucent so as not to interferewith post-operative imaging procedures, or can be partially radiopaqueand partially radiolucent. Exemplary materials that can be used inconstructing the implantable device include metals such as titanium orstainless steel, non-resorbable polymers and composites such aspolyetheretherketone (PEEK) and carbon-fiber reinforced PEEK, resorbablepolymers such as polylactic acid and polyglycolic acid, ceramicmaterials such as aluminum oxide and hydroxyapatite, allograft materialsderived from animal or human cortical or cancellous bone, and/or anycombination thereof.

In one embodiment, the shaft of the implantable device can be 2-4 mm inheight (i.e., Y dimension), 4-12 mm in width (i.e., X dimension), and2-8 mm long. The implantable device can be sized so as to be insertablethrough an access port as part of a minimally invasive procedure.

In certain embodiments, the edges of the shaft that will contact theinterior walls of a bone opening can be shaped to mate or otherwisesubstantially conform to the dimensions of the bone wall surface to helpthe device maintain a desired position both during the procedure andpost-operatively. In one embodiment, these edges can be conformable tothe interior walls of a bone opening by pre-attaching HEALOS(HA/collagen sponge) pieces thereto. HEALOS is an osteoconductive matrixconstructed of cross-linked collagen fibers that are fully coated withhydroxyapatite and is available from DePuy Spine, Inc. of Raynham, Mass.Such pre-attached pieces can have the effect of promotingosteointegration between the implantable device and the surroundingbone. Alternatively, the edges can be coated with hydroxyapatite and/ora porous metal or polymer coating to elicit the same effect.

In use, the implantable device 100 can be inserted into a relativelysmall opening formed in a lamina to force a portion of the lamina awayfrom the spinal canal, thereby increasing the cross-sectional size ofthe spinal canal. In a typical laminoplasty procedure, as shown in FIG.3A, a blind recess or “green stick” 118 is formed on a first side of alamina 120 of a vertebral body 122 to act as a hinge. On a second sideof the lamina 120, opposite the side containing the blind recess 118, anopening or osteotomy 124 is formed all the way through the lamina 120 tothe dura of the spinal canal 126. With the vertebral body 122 preparedas described, the implantable device 100 can be advanced into theopening 124 towards the spinal canal 126 in the direction of arrow 128.The head 102 of the implantable device 100 can be made wider than theshaft 104 to prevent over-insertion. As shown, the leading edge of thehead 102 will contact the mouth of the opening 124 before the distalbulleted tip 130 of the shaft 104 advances too far into the spinal canal126, precluding further distal movement and providing the surgeon withmechanical feedback as to the position of the implantable device 100within the opening 124. In the illustrated embodiment, the implantabledevice 100 has a first dimension Y that is slightly larger than thewidth of the opening 124. As the implantable device 100 is advanced intothe opening 124, its bulleted tip 130 acts as a wedge or camming surfaceand causes a partial expansion of the opening 124. As shown in FIG. 3B,this dimensional arrangement causes the lamina 120 to move posteriorlyaway from the vertebral body 122 as the implantable device 100 isinserted, hinging about the blind recess 118. Although in theillustrated embodiment the dimension Y of the shaft 104 is greater thanthe width of the opening 124, this need not always be the case. Rather,the dimension Y can be less than or substantially the same as the widthof the opening 124, allowing the implantable device 100 to be insertedin a clearance fit.

With the implantable device 100 inserted into the opening 124, it canthen be rotated in the direction of arrow 132, as shown in FIGS. 3B-3E.The implantable device 100 is shown in FIG. 3C inserted into the opening124 in a first orientation. In FIG. 3D, the implantable device 100 isshown after having been rotated ninety degrees. As shown, because theshaft 104 of the implantable device 100 has a cross-section with a firstdimension distinct from a second dimension, rotation of the device 100within the opening 124 causes the width of the opening to expand. Asshown in FIG. 3E, the lamina 120 is pushed further away from thevertebral body 122 by rotation of the implantable device 100, resultingin an increase in the cross-sectional size of the spinal canal 126.

In one exemplary embodiment, either the shaft or the head of theimplantable device can include at least one lateral extension extendingfrom a proximal end thereof to facilitate securing the implantabledevice to bone. In FIG. 4A, an implantable device 200 is shown having alateral extension 234. The lateral extension 234 extends from a proximalend of the implantable device 200 over an outer bone surface 236 of thevertebral body 222. The lateral extension 234 can include at least oneopening formed therein for receiving at least one fastening element 238.In the illustrated embodiment, the fastening element 238 is a threadedbone screw. A person skilled in the art will recognize however thatvirtually any type of fastening element known in the art can be employedto secure the implantable device 200 to the vertebral body 222. Forexample, the fastening element 238 can be a nail, hook, rivet, staple,etc. In another embodiment, the lateral extension 234 can be configuredto receive more than one fastening element, or the implantable device200 can have more than one lateral extension. As shown in FIGS. 4B-4E,the at least one opening in the lateral extension can have a variety offorms. In FIG. 4B, one embodiment of a lateral extension 234 is shownthat has a single opening 240 formed therein. The opening 240 is a roundbore hole that can conform to the diameter of the fastening element tobe used. In FIG. 4C, another embodiment of a lateral extension 234′ isshown that has multiple openings 240′ therein. FIG. 4D shows yet anotherembodiment of a lateral extension 234″ wherein the opening 240″ is inthe form of an elongate slot. Such embodiments provide for increasedflexibility in the placement of the fastening element, since thefastening element can be placed anywhere along the length of theelongate slot. In FIG. 4E, another embodiment of a lateral extension234′″ is illustrated that has an opening 240′″ configured to allowpolyaxial fastening of the implantable device to bone. As shown in FIG.4E, the proximal surface of the lateral extension 234′″ has a sphericalrecess 242 formed therein for receiving the head of a polyaxial fastener243. In addition, the distal surface of the lateral extension 234′″ hasa corresponding frusto-conical recess 244 configured to further increasethe range of angles at which a polyaxial fastener 243 can be insertedthrough the lateral extension 234′″. Embodiments of the lateralextension can also include any combination of the various opening typesdescribed herein.

In yet another embodiment, the implantable device can include lateralextensions that are attached thereto with a hinge. An implantable device300 is shown in FIG. 5A inserted into an opening 324 in a lamina 320. Asshown, the implantable device 300 can include a hinge body 344 attachedto a proximal end of its head 302. The hinge body 344 can have one ormore hinged plates 346 attached thereto. The hinge body 344 can beintegral with the implantable device 300, can be permanently attachedthereto, or can be selectively attached thereto. In the illustratedembodiment, the hinge body 344 is selectively attached to theimplantable device 300 using a fastening element 348. Other means ofattachment include riveting, stapling, gluing, welding, sonic welding,or any other attachment means known in the art. In addition, the hingeplates 346 can be attached to the hinge body 344 using a variety ofhinge types. In one embodiment, as shown in FIGS. 5B and 5C, the hingebody 344 and the hinge plate 346 can each include one or morecorresponding tubular protrusions 348 a, 348 b through which a hinge pin350 can be inserted to form a hinge between the hinge body 344 and thehinge plate 346. In another embodiment, as shown in FIG. 5D, the hingebody 344′ and the hinge plate 346′ can be formed integrally and can havean area of decreased thickness 352 along which the two may hinge.

The hinge plates 346 are shown in FIG. 5A in a first, folded positionand again in FIG. 5E in a second, unfolded position. As shown, when thehinge plates 346 are unfolded, they can be fastened to a portion of thelamina 320 and/or the vertebral body 322 adjacent to the opening 324using any of a variety of known fasteners, such as bone screws, rivets,staples, etc. The hinge plates 346 can have openings formed therein asdescribed above with respect to the lateral extensions 234 shown inFIGS. 4A-4E.

In use, the implantable device can be inserted into the opening 324 androtated to push the lamina 320 away from the vertebral body 322, therebyexpanding the cross-sectional size of the spinal canal 326. The hingebody 344 and hinge plate 346 assembly can then be positioned adjacent tothe implantable device 300 and affixed thereto using a fastener 348. Thehinge plate(s) 346 can then be unfolded and fastened to the vertebralbody 322 and/or the lamina 320. In embodiments where the hinge body 344is formed integrally with the implantable device 300, the openings inthe hinge plate(s) 346 can be sized to permit an insertion apparatus 108to be passed through the folded hinge plate(s) 346 and to selectivelycouple to the implantable device 300, as shown in FIG. 5F.Alternatively, when an insertion apparatus 108′ is used, the hingeplate(s) 346 can be sized such that the opposed claws of the insertionapparatus 108′ can be selectively coupled to the implantable device 300,around the hinge plate(s) 346 when they are in a folded position, asshown in FIG. 5G. One advantage to the hinge plate embodiments is thatthe implantable device and/or hinge body and hinge plate assembly can beinserted through the narrow confines of a working channel of a minimallyinvasive access device, such as a cannula or tubular port.

In another embodiment, as shown in FIG. 6A, the implantable device 400can include a sleeve 456 disposed therearound. As shown in FIGS. 6B-6C,the sleeve 456 can be configured to remain in a fixed position withinthe opening 424 in the lamina 420 while the implantable device 400 isfree to rotate. In the illustrated embodiment, a point A on the sleeve456 is shown to remain in the same position, despite the implantabledevice 400 having been rotated 90 degrees in the clockwise direction. Insuch embodiments, the implantable device frictionally slides along aninterior surface of the sleeve 456, rather than along an interiorsurface of the bone opening 424. The sleeve 456 can be formed of alow-friction material or can include a low-friction coating appliedthereto, thereby reducing the rotational force required to manipulatethe implantable device 400. Alternatively, or in addition, part or allof the surface of the sleeve 456 can be coated or formed from anosteointegration promoting material such as HEALOS. One skilled in theart will appreciate that a variety of biocompatible materials can beused to form the sleeve, including metals, metal alloys, polymers, andceramics. As shown in FIGS. 6B-6D, the sleeve 456 can be expandableand/or flexible so that when the implantable device 400 is rotated toexpand the spinal canal 426, the sleeve 456 likewise expands andotherwise remains in position within the opening 424.

In use, the sleeve 456 can be positioned around and/or pre-attached tothe implantable device 400 first, and the two can then be inserted as apair into the opening 424. Alternatively, the sleeve 456 can be firstinserted by itself in the opening 424 and then the implantable device400 can be inserted within the sleeve 456 thereafter. In the latterembodiment, the sleeve 456 can have a flanged portion at its proximalend (not shown) sized larger than the width of the opening 424 toprevent over-insertion of the sleeve 456 into the spinal canal 426,similar to the proximal head of the implantable device discussed above.

Various methods for expanding a spinal canal are also provided. In oneembodiment, a patient's spine is accessed using one or moreminimally-invasive techniques known in the art. For example, a smallincision can be made in a patient's neck or back and a trocar or cannulacan be inserted therethrough to provide a working channel through whicha surgeon can access the patient's spine. The surgeon can then pass oneor more suitable instruments through the working channel to form anosteotomy or opening in one side of a lamina of one of the patient'svertebrae. The osteotomy can be in the form of an opening formed all theway through the lamina to the dura of the spinal canal. Using the sameor a second access portal, the surgeon can also form a blind bore or“green stick” in a second side of the lamina to act as a hinge.

With the patient's vertebra prepared as described, the surgeon caninsert an implantable device (e.g., using the same cannula used toaccess the surgical site and form the osteotomy) described herein intothe osteotomy. The surgeon can first selectively couple the implantabledevice to an insertion apparatus as described above and then pass theelongate body of the insertion apparatus and the implantable devicethrough the working channel, keeping the handle and trigger of theinsertion apparatus outside of the patient. Using an imaging techniquesuch as fluoroscopy and/or mechanical feedback, the surgeon can advancethe distal bulleted tip of the implantable device into the osteotomy. Inone embodiment, the implantable device and osteotomy can be sized suchthat merely inserting the implantable device, without rotating it, iseffective to partially expand the osteotomy and the spinal canal.Alternatively, the implantable device can be sized to fit within theosteotomy in a clearance fit. The implantable device can be advanceddistally into the osteotomy until the head of the device contacts anouter surface of the vertebra, preventing further distal advancement ofthe implantable device. The surgeon can then rotate the handle of theinsertion apparatus 90 degrees, effecting a similar 90 degree rotationof the implantable device within the osteotomy. Since the shaft of theimplantable device has a first dimension distinct from a seconddimension, rotation thereof within the osteotomy can cause the osteotomyand therefore the spinal canal to expand in size.

In some embodiments, rotating the implantable device within theosteotomy can cause one or more arcuate protrusions formed on theimplantable device to bite into the surrounding bone, thereby minimizingthe risk of undesirable post-operative movement of the device. Rotatingthe implant can also cause the cut ends of the lamina on either side ofthe osteotomy to cam over one or more radiused edges of the implantabledevice.

Having rotated the implantable device 90 degrees, the surgeon canactuate a component (e.g., a trigger) of the insertion apparatus todetach it from the implant. The insertion apparatus can then bewithdrawn from the working channel, leaving the implantable device inthe patient's spine. The surgeon can then remove any other tools ordevices used in the procedure and close the incision(s).

In some embodiments, methods for expanding the spinal canal can includesecuring the implant to bone to prevent post-operative movement of theimplantable device. In such embodiments, the surgeon can pass a fastenerthrough the working channel and can fasten a lateral extension of theimplantable device to a bone surface adjacent to the osteotomy. Inanother embodiment, securing the implant to bone can include unfoldingone or more hinged lateral extensions and then fastening them toadjacent bone as described herein. The hinged lateral extensions can beformed integrally with the implantable device, in which case the devicecan be initially passed through the working channel with the hingedextensions in a folded position using an insertion apparatus similar tothat described above in FIGS. 5F and 5G. In embodiments where the hingedlateral extensions are not formed integrally with the implantabledevice, the device can optionally be implanted first by itself. Thesurgeon can then pass the hinged lateral extensions and/or the hingebody through the working channel and attach them to the implantabledevice already inserted into the patient's spine.

Methods for expanding the spinal canal can also include the use of asleeve disposed around the implantable device to allow the implant torotate within the sleeve rather than within the opening in the lamina.In one embodiment, the sleeve can be positioned around the implantabledevice prior to inserting it into the opening in the lamina. Once thesleeve and the implantable device are simultaneously inserted, thesleeve can stay in position while the implantable device is rotatedtherein. In another embodiment, the sleeve can be inserted into theosteotomy first, prior to inserting the implantable device. In suchembodiments, the surgeon can advance the sleeve distally into theosteotomy until a flanged portion at the proximal end of the sleevecontacts the outer surface of the lamina, preventing further distaladvancement. The implantable device can then be advanced into the sleeveand rotated as described above.

In some embodiments, methods for expanding the spinal canal can includebilaterally expanding the spinal canal by distracting the lamina fromboth sides. As shown for example in FIG. 7, two osteotomies 524 can beformed, one on each side of the lamina 520. Two implantable devices 500can then be used to bilaterally expand the spinal canal 526,substantially as described above with respect to single-implantembodiments. Although an implantable device having hinged lateralprotrusions is illustrated, any embodiment of the implantable device canbe used for bilaterally expanding the spinal canal. In addition, thebilateral expansion need not always be symmetrical as shown. Rather,implantable devices of differing sizes may be used on either side of thevertebra to achieve an asymmetrical distraction of the lamina.

While use of the implantable device in the spine is discussed at lengthherein, the device can be used in almost any portion of a patient, andits use is not by any means limited to within the spine. Additionally, aperson skilled in the art will appreciate that, while the methods anddevices are described in connection with minimally invasive procedures,the methods and devices disclosed herein can be used in any kind ofsurgical procedure, including open surgery.

One skilled in the art will appreciate further features and advantagesof the invention based on the above-described embodiments. Accordingly,the invention is not to be limited by what has been particularly shownand described, except as indicated by the appended claims. Allpublications and references cited herein are expressly incorporatedherein by reference in their entirety.

What is claimed is:
 1. An implantable device for expanding a spinalcanal, comprising: an elongate body having a head and a shaft and alongitudinal axis; the shaft having a cross-section taken perpendicularto the longitudinal axis such that the longitudinal axis is normal to aplane in which the cross-section lies, the cross-section having a lengththat is distinct from a width and having two diagonally-oppositeradiused corners and two diagonally-opposite non-radiused corners, andthe head having at a proximal end thereof a driver interface with atorque receiving surface; wherein the head is formed at a proximal endof the elongate body and a distal end of the elongate body is bulleted.2. The device of claim 1, wherein the cross-section of the shaft issubstantially rectangular.
 3. The device of claim 1, wherein the bodyincludes an osteointegration-promoting coating.
 4. The device of claim1, wherein the head has a dimension larger than the shaft such that itis configured to prevent over-insertion of the body into an opening. 5.The device of claim 1, wherein the elongate body has at least onearcuate protrusion formed thereon configured to engage bone as the bodyis rotated within an opening.
 6. The device of claim 1, furthercomprising a sleeve disposed around the body such that the body isrotatable within the sleeve.
 7. The device of claim 1, wherein the bodyis formed of a resorbable material.
 8. The device of claim 1, whereinthe body includes at least one lateral extension at its proximal end,the lateral extension having at least one opening formed therein forreceiving at least one fastening element.
 9. The device of claim 8,wherein the opening in the at least one lateral extension comprises anelongate slot.
 10. The device of claim 8, wherein the opening in the atleast one lateral extension comprises a polyaxial seat.
 11. The deviceof claim 8, wherein the at least one lateral extension is attached tothe proximal end of the body with a hinge such that the extension isrotatable about the hinge.